Noninterfering electrical signaling system



4 Sheets-Sheet 1 n M. w. MUEHTER NONINTERFERING ELCTRICAL SIGNALINGSYSTEM March 10, `197|() Filed oct. 21, 1966 March 10, 1970 M. W.MUEHTER NONINTERFERING ELECTRICAL SIGNALINGKSYSTEM Filed Oct. 21. 1966TIIZC 4 Sheets-Sheet 2 FIG2.

23 -b ro coNTAc'r 'rx-l TIMING RELAY CONTROL CIRCUIT ANTI-JAMMING cmcunl March 10, 1970 M. w. MUEHTER 3500,377

NONINTERFERING ELECTRICAL SIGNALING SYSTEM 4 Sheets-Sheet 3 Filed oct.v21, 196e M. W. MUEHTER NONINTERFERING ELECTRICAL SIGNALING SYSTEM Filed0st. 21. 1966 March 10, 1970 I v 4 Sheets-Shed. 4

nited States Patent Oliice 3,500,377 Patented Mar. 10, 1970 3,500,377NONENTERFERING ELECTRICAL SIGNALING SYSTEM Manfred W. Muehter,Livingston, NJ., assignor to American District Telegraph Company, JerseyCity, NJ., a corporation of New Jersey Filed Oct. 21, 1966, Ser. No.588,517 Int. Cl. G08b 25/00 U.S. Cl. 340-287 4 Claims ABSTRACT OF THEDISCLOSURE An electrical protection system consisting of a plurality ofline circui-ts connected to a central station, and a plurality oftransmitters associated with each line circuit, in which interferencebetween actuated transmittersl on -different lines is prevented bygiving precedence in establishing a connection to the central station tothat line which is the rst to -have an actuated transmitter, and byallowing all actuated transmitters on the line having precedence tocomplete their transmission to the central station before another lineis connected to the central station. This system is also characterizedby an antijamming circuit which provides for bypassing a stalledtransmitter on a given line so that other transmitters associated withthat line are given access to the line ahead of the stalled transmitter.This system is further cha-racterized by a limiter circuit forpreventing damage to the system, in which both the line current and theline voltage are limited to respective predetermined maximum levels.

The present invention relates to electrical signaling systems and moreparticularly to electrical signaling systems of the positive,noninterfering, successive type.

In circuit type electrical protection systems, a place to be protectedis provided with a protection c-ircuit including one or more detectiondevices each arranged -to transmit a characteristic alarm signal uponactuation. An alarm signal usually consists of a series of electricalpulses which form a code identifying the na-ture and source of thesignal and which may be annunciated audibly and visually at thereceiving end of the system as well as recorded to form a permanentrecord.

Such signaling systems have been known and used with gratifying resultsfor many years in the rendering of electrical protection services,particularly for large industrial companies and government complexeswhich have so many signal transmitting devices in service as to warrantthe maintenance of a signal receiving and control center on the premiseswhich `is staffed by personnel trained to take the appropriate actiondemanded by the nature of the signals receivedpSystems of this type areknown as proprietary installations and are commonly designed to receiveand record alarm type signals originating from a variety of detectiondevices such as, for example, manual re alarm boxes, automatic redetection devices, waterow alarm detectors associated with au-tomaticsprinkler systems and burglar alarm devices. Provision is also made forthe receipt of supervisory signals such as those emanating fromwatchmens reporting systems and signals indicating the condition of-thetvarious elements of sprinkler systems such as the positions ofvalves, the level and temperature of the water supply and the air andwater pressures in the system.

Since proper response .to an alarm signal requires immediate andpositive identification of the actuated device, -it is imperative lthatin the event that more than one device is actuated, the signalsgenerated by each actuated device be received without interfering withone another. It is possible, of course, to provide a separate signalpath between each device and the receiving center, but this requires acomplex and costly in-stallation at :the protected premises.

In order to prevent mutual 4interference at a reasonable cost,s'o-called positive noninterfering successive signaling systems havebeen developed. Such systems permit the signals from a number ofactuated devices to be transmitted one after the other over the samesignal path without interfering with one another, by holding up thetransmission of signals from all succeeding devices until lthe precedingdevice has finished transmitting its signal.

In the present invention, there is provided a positive, noninterferingsignaling system having several unique features. The system of thepresent invention includes a number of line circuits, each -line circuithaving a number of transmitters. ln order to prevent interferencebetween signals from transmitters on different circuits, a line control-circuit connects the line having the first actuated transmitter to thecontrol center, and all other line circuits are prevented from beingconnected to the control center until all actuated transmitters on theconnected line circuit have completed their transmission of signals.This feature of preventing intereference between lines is to bedistinguished from the above-mentioned prior art systems for preventinginterference between transmitters on the Isame line.

Ordinarily, if a detection device is in good working order, itstransmitter will send an alarm signal for a selected interval of time,after which it will stop and be disconnected from the line, thereby toLpermit another actuated device on the same line to start transmittingits alarm signal over the line. However, if through a mechanical orelectrical fault the device already on the line is jammed or stuck sothat it stops transmitting a coded signal but fails to turn off, it willhold the line and prevent any other actuated device on the line fromtransmitting. In the present invention, a stalled transmitter isautomatically removed from the line after the transmitter has beenstalled for a predetermined interval of time. This is accomplished by anovel antiejamming circuit arrangement in which other devices that havebeen actuated are given access to the line in a manner which assigns thestalled transmitter the lowest priority among the actuated devices sothat the jammed transmitter is not reconnected to the line until afterall other actuated devices have been connected to the line. Theanti-jamming circuit of this invention automatically removes a stalledtransmitter from the line by switching the line to receive power fromthe opposite end of the line so that other transmitters are given accessto the line ahead of the stalled transmitter.

An additional feature of this invention is a limiter circuit of novelstructure for protecting the system and various components thereof frompossible damage by limiting the line current to a predetermined maximumlevel, and for reducing the undesirable effects of multiple lineleakages to ground by reducing the line voltage to a selected level whenthe line is switched to the receiving center.

The invention will be fully understood from the following detaileddescription of illustrative embodiments thereof taken in connection withthe appended drawings, in which:

FIG. 1 is a block diagram illustrating a complete signaling systemembodying the principles of this invention;

FIG. 2 is a diagram of the limiter circuit of the system shown in FIG.l;

FIGS. 3A and 3B are schematic diagrams illustrating in detail certainportions of the system shown in FIG. l;

3 FIG. 4 is a diagram indicating the positions of the FIG. 3A and 3Bdiagrams relative to one another; and

FIG. 5 is a diagram of the anti-jamming circuit of this invention.

Complete signaling system Referring first to FIG. 1, power to operatethe system is drawn from a power supply 10, which for example, mightconveniently consist of a 48 volt battery located at the control center100 and aranged to be trickle charged from locally available power linessuch as 110 volt A.C. lines (not shown). Also incorporated in the powersupply is a D.C. to D C. converter to provide a separate D.C. voltagesource for each line circuit 1 through 4, say 94 volts, for variouspurposes as will be made apparent hereinafter.

The various detection and supervisory devices of the electricalprotection services and their associated transmitters are seriesconnected in loops which are identified on the drawing as line circuits1, 2, 3, 4. It is to be understood, of course, that this invention isnot limited to any particular number of line circuits, the number fourbeing chosen only for illustrative and descriptive purposes.

A line control circuit 110 is provided at control center 100 for eachpair of line circuits: thus line circuits 1 and 2 are shown connected tothe line control circuit 110 and line circuits 3 and 4 are shownconnected to line control circuit 110. Each line circuit may include anycombination of a variety of electrical protection service devices, eachdevice being provided either with its own code signal generatingmechanism or with a transfer contact which is operated when thedetection device responds to the condition intended to be detected, theoperation of the transfer contact resulting in the actuation of anassociated code signal generating mechanism or transmitter.

As an example of the variety of devices which may be included within asingle line circuit, line circuit 1 (reading in the clockwise direction)is shown as including a manual fire alarm station 12 of the coded typewhich contains the actuating device (not shown) and the code signaltransmitter in the same unit. Next is shown a noncoded supervisorydevice 13, for example, a gate valve or water level detector connectedby means of a short cable to the associated code signal transmitter 14a.Although the device 13 does not produce coded signals, the operation ofthe device 13 will operate a transfer contact which in turn will actuatethe associated transmitter 14a to produce a coded signal indicative ofthe general area in which the actuated device 13 is located. Theactuation of transmitter 14a and the other transmitters by operation ofa transfer contact is described in detail below in connection with theexplanation of FIGS. 3A and 3B. A burglar alarm system 15, which mightconsist of a number of simple door and window supervisory devices aswell as more complex photoelectric and ultrasonic intrusion detectionsystems, is connected to an associated code signal transmitter 14b, forexample, through a control unit (not shown) which is equipped with arelay having a transfer contact to actuate the associated transmitter14b. The next code signal transmitter 14C generates alarm type signalsin response to the actuation of devices of various types in an automaticwater-flow alarm service 16, the individual devices being connected totransmitter 14e` through a control relay having transfer contacts whichoperate transmitter 14e. Similarly, transmitter 14d generates codesignals in response to the operation of a relay by actuation of suchdevices as water level, temperature and valve position indicatordevices. A number of different types of automatic fire detectionservices 18 are connected through a suitable control unit (not shown)having a suitable relay with transfer contacts to operate transmitter14e. These services include such devices as thermostats, smoke detectorsand pneumatic fire detection apparatus. The industrial supervisionservices indicated by element 19 comprise various process supervisorydevices designed to monitor temperature, pressure, shaft rotation, andother parameters, and these devices are shown connected to thetransmitter 14f, there being an intermediate control circuit (not shown)with a relay whose transfer contacts operate the associated transmitter147. The last transmission device, denoted by the reference numeral 20,is representative of night watch service stations incorporating theirown transmitters and employed by watchmen to signal their progress alongprescribed patrol routes.

lf desired, the code signal generators may be of essentially the samedesign, and may employ any one of a number of conventional code signalgenerating arrangements, such as a commutator type of code signalgenerator, to generate a series of current pulses according to apredetermined code. If further desired, the code signal generatingdevice may be designed to repeat the code signal for a selected numberof times so that a selected number of signal rounds are transmitted uponeach actuation of the associated detection device.

It will be understood that other and usually more complex combinationsof alarm and supervisory devices as well as branch circuits would beemployed in an actual installation. The preceding example therefore isintended for illustrative purposes only and not as a limitation upon thepresent invention.

As hereinbefore mentioned, line control circuit is designed toaccommodate two line circuits, line circuits 1 and 2, and it is to beunderstood that line circuit 2 may have coupled thereto any combinationof the various electrical protection apparatuses described in connectionwith line circuit 1. Since the transmitter on the line circuits do notdraw power except when operating, and since (except for the startinginterval when several transmitters may draw a small limited currentsimultaneously as explained more fully below) only one transmitter canoperate at a time, a large number of devices may be connected to a line,the total number on a single line being limited primarily by theelectrical resistance of the line and the locations of the devices.Therefore, according to the location ofthe various transmitters and theresistance of the line circuits involved, sufficient line circuits areprovided to take care of all the installed devices. Provision thereforehas been made to accept in modular fashion additional line circuits suchas line circuits 3 and 4, together with associated' line controlcircuits such as that indicated by line control circuit 110. Regardlessof the number of line circuitsV thus added, the entire system isdesigned to operate on a noninterfering basis, with the coded alarmsignals being received in the predetermined order in which thetransmitters are connected to the line circuit in the event that morethan one transmitter is operated at the same time.

The line control circuits 110, 110 connect the line circuits to the maincontrol circuit 21 where the code signals are translated into the properform for the operation of printer 22, lamp panel 23, and tapper bell 24.Additional lamp panels such as that indicated by panel 23', which isalso of modular design, may -be added as necessary to accommodateadditional line circuits. Printer 22, panel 23 and bell 24 are ofconventional construction, and provide visible and audible indicationsof the actuation of the detection devices. For example, all incomingcode signals and the time and date of receipt are recorded by theprinter 22, and except for night watch signals, may also be annunciatedby a buzzer and pilot li'ght. The operator may acknowledge the receiptof such signals by means of a manually operated switch in the maincontrol circuit 21 which silences the buzzer and, after the signaltransmission is complete, causes the printer 22 to record anacknowledgement code signal and the time. In the case of alarm signalsonly, tapper bell 24 repeats the code signal received to insure that theoperator`s attention is directed to the receipt of av signal of'emergency nature.

The coded alarm signals may 'be printed on a paper tape in any one of anumber of forms, such as a group of letters and numbers inwhich theletters identify the particular service, for example, manual fire alarm,sprinkler supervision, or the like, and the numbers indicate the areaand particular box identification as well as the time and date of thesignal. Alarms, supervisory and restoration signals may be furtherdistinguished by the number of rounds or repetitions of the code signalwhich are recorded. Timing modules and relays in the main control panelrespond to the code signal to set up circuit paths to the solenoidscontrolling the printer keys and the buzzer and lamp features. Forexample, the location portion of the signal code may be transmitted as aselected number of pulses of equal duration which are counted by amagnetic counter in the main control circuit to activate the properprinter solenoids and to pulse the tapper bell.

Turning now to FIGS. 3A and 3B, which illustrate apparatus connectedtogether in the relationship indicated by FIG. 4, the Ibasic module ofthe system of this invention comprises two independent line circuitswhich are designated line circuit 1 and line circuit 2, each linecircuit being provided with two loops, an A loop and a B loop. Thevarious transmitting devices in each line circuit are connected acrossboth the A and B loops of the corresponding line circuit. To simplifythe drawing, only transmitter 2-1 of line circuit 1 is shown in detail,and it will be understood that all other transmitters such as 1-1 and3-1 in line circuit 1 and 1-2 through n-2. in line circuit 2 are similarthereto in construction and in their connection to the correspondingline circuits. As shown in FIG. 3A, transmitters 1-1, 2-1, 3-1 areconnected across the A and B loops of line circuit 1 in that order, sothat if two or more transmitters are actuated at the same time, the lownumber transmitter sends its signal first, followed by the next highernumbered transmitter and so on.

At control center 100, there is provided for each line circuit 1, 2 aseparate source of potential 31-1, 31-2, for supplyingr starting currentto the associated line circuit 1 and line circuit 2 respectively, wherethe potential conveniently might be 94 volts D.C. The potential sourcesare ungrounded so that a single ground fault, even on more than one linesimultaneously, will not affect the operation of the system. Othersources of potential at control center 100 include source 44 connectedbetween points 44a and 44b, and source 45 connected between points 46and 47, as will be described hereinafter.

The current path through line circuit 1 may be traced from positiveterminal 32-1 of potential source 31-1 via a conductor 33 to currentlimiter circuit 34-1. The function of current limiter circuit 34-1 is torestrict the line current to a predetermined level, say, 46milliamperes, and thus protect the system from such damage as mightarise from accidental short circuits, as well as to prevent an excessivecurrent supply to the transmitter motors where the series resistance ofthe line is low. From current limiter circuit, 34-1, the current pathcrosses through conductor 36 via the normally closed back contact N1-1of the noninterference relay N1 in line control circuit 110 and thencethrough the transmitters 11, 2-1, 3-1. Within each transmitter, asillustrated by transmitter I2-1 in the drawing of FIG. 3A, the presenceof rectifier REC-6 causes the current to pass through a branch path viathe normally closed contact Kl-Z Which is cam operated by thetransmitter motor M. The branch path rejoins the conductor 36 at a pointjust past rectifier REC-3 and continues through the remainingtransmitters connected to the line circuit as indicated by transmitter3-1. At the last transmitter, here indicated as transmitter 3-1,conductor 36 is brought back to the control center 100, thus forming aloop designated as A on the drawing. At control center 100, the paththen passes through make contact M1-3 of relay M1 to the first windingS1-W1 of the normally energized line supervisory relay S1-1 and back outthrough all the transmitters and again returning by way of conductor 36to establish the loop designated B via the normally closed back contactN1-2 of the noninterference relay N1. Conductor 33 completes the pathfrom the starting relay delay circuit 37-1 to the negative terminal 35-1of the potential source 31-1. The starting relay delay unit 37-1 is atransistor operated unit which includes the second winding S1-W2 of theline supervisory relay S1-1 and the winding ST1-W of the starting relayST1.

Line circuit 2 is identical to line circuit 1 described above, save thata different number of transmitters may be connected thereto as may bedesired for a particular installation. Corresponding relays and contactshave been denoted by the sufx Z. Thus the noninterference relay N2 andits contacts N21, N2-2, correspond t0 relay N1 and contacts N1-1, N1-2,of line circuit 1. The front contact of N2-1 is connected to the frontcontact of N1-1 by conductor 39 and the front contact of N1-2 isconnected to the front contact of N2-2 by conductor 40.

-Suppose now that a detection device of some sort connected totransmitter 2-1 of line circuit 1 is actuated and thereby an associatedrelay (not shown) transfers itsl armature 41 to Contact point 42. Astarting current path is thus completed from positive terminal 32-1 ofpotential source 31-1 to negative terminal 35-1 via the |back contactN1-1, rectifier REC-7, resistor RX-30', armature 41 of the actuatingdevice relay, contact point 42, back contact K2-1 of a cam operatedtransfer contact controlled by the transmitter motor M, resistor RX-S(connected in parallel with thermistor SR provided to compensate fortemperature caused capacitance variation of capacitor CD-l), adjustableresistor RX-6, the winding of a reed relay R, rectifier REC-8 to thenegative B loop and thence Via back contact N1-2 and the starting relaydelay circuit 3'7-1 to the negative terminal 35-1. A rectifier REC-27provides an alternate starting current path from the A loop to the Bloop which is employed when the line has an open fault requiringoperating potential to be supplied to the transmitter from the other endof the line.

A first charging or starting path is also completed by the transfer ofarmature 41 to contact point 42, from contact K2-1 to a capacitor CD-1and thence to the negative B loop via the rectifier REC-8. The capacitorCD-l is in parallel with the series combination of contact R-l of reedrelay R and the motor M. Due to the current limiting action of limitercircuit 34-1 and the combined resistance of the line and resistorRX-30', capacitor CD-1 will begin to charge gradually. Resistor RX-30performs the important function of allowing morev remote transmitterssuch as transmitter 3-1 to function in the event that transmitter 2-1should become stalled with the contact K1-1 closed, as explained morefully below. Without resistor RX-30, the shunt established by contactK1-1 would not allow sufficient current to flow out through the line tocharge the corresponding capacitor of a more distant transmitter.

The resistance of resistor RX-G is adjusted so that reed relay R willoperate when the voltage of capacitor CD-1 reaches a selected level,say, approximately 20 volts. When relay R operates, its contact R-lcloses to complete three electrical paths:

(l) between the A and B loops via rectifier REC-4 and resistor RX-7;

(2) between capacitor CD-1 and motor M;

(3) between capacitor CD-1 and the coil of relay R.

The completing of a path between the A and B loops via rectifier REC-4and resistor RX-7 blocks the charging path for capacitor CD-l by backbiasing diode REC- 8, since the voltage across resistor RX7 is muchlower. Capacitor CD-l therefore receives a xed charge regardless ofeither the location of the transmitter on the line or the lineresistance.

Blocking of the charging path for capacitor CD-1 causes CD-l to start todischarge, and the completed path between capacitor CD-1 and motor M viacontact R-l causes motor M to start running in the first stage orstarting interval of a twostage operation. Shortly after the motor hasstarted running, a first cam (not shown) mechanically associated withmotor M operates the contacts Kl-l, Kl-Z and K1-3. The operation of K1-2opens the line to other transmitters located further out on line circuit1, rectitier REC-6 being in the opposing direction. The operation ofcontact K1-1 completes a shunting path between the A and B loops viapoints 25 and 26 and rectifier REC-7 and the current limiting resistorRX-30, thereby completely shunting down the current supply to thetransmitter. The closure of contact K1-3 introduces the coding mechanism27, shown symbolically by contacts 27-1, 27-2, into a circuit couplingthe A and B loops via capacitor CD-l and contact Kl-l at point 26.However, this circuit does not receive current until diode REC-6 ordiode REC-3 conducts, depending from which side current is supplied. Themotor M, now bypassed by the closure of contacts K11, therefore receivesno current from the line, and the tixed charge on capacitor CD-l issucient only to drive the motor M to a second starting position where ithalts until the line potential is reversed. The relay R remainsenergized by capacitor CD-l via contact R-l until capacitor CD-l hasbeen nearly discharged, at which point relay R releases.

The increased curent ow in the line circuit conductor 36 resulting fromthe closure of contact K1-1 acts as a trigger signal which is detectedby conventional means in the starting relay delay unit 37-1 and isemployed rst to energize the'second winding S1-W2 of the linesupervisory relay S1-1 and, after a delay, then to energize the windingST-Wl of starting relay ST. The energizing of winding S1-W2 prevents therelease of relay S11 and a consequent false indication of an opencondition in the line circuit as would otherwise occur, since theprimary winding S1-W1 is now deenergized by the opening of contact K1-2.After a delay of about four seconds provided by a device such as aresistancecapacitance network in unit 37-1 (not shown), the startingrelay ST1 is energized. The purpose of the delay period is to allowadequatetime for the corresponding capacitor CD-l in each actuatedtransmitter to become sufliciently charged since relay ST1 wouldotherwise be prematurely energized by the initially high chargingcurrent of any one of the capacitors CD-1.

Within line control circuit 110, the transfer of contact ST1-1 ofstarting relay ST1 completes a circuit to the winding of thenoninterference relay N1 from the 48 volt D.C. source 44. Anoninterference relay N1, N2 is provided for each line circuit 1, 2,respectively, and all are parallel connected across the 48 volt source44 through the N relays reset circuit 49. To illustrate the functioningof the noninterference principle, two additional noninterference relaysN3 and N4 are also shown, such as would be provided for two additionalline circuits illustrated as line circuits 3, 4 shown in FIG. 1.

The transfer of contact ST1-1 opens the positive supply path to all ofthe noninterference relays on one side of relay N1, here shown to theright, and not only is relay N1 locked in to source 44 through theoperation of its own contact N1-3, but also contact N144 opens toprevent the restoration of the path to source 44 to the other N relayseven after the starting relay ST1 is released. At the same time, contactN1-5 opens to prevent the operation of all noninterference relays on theother side of relay N1, here shown to the left. In the case of relay N1,there are no other relays to the left, but in the case of another Nrelay, the opening of the corresponding contact would prevent subsequentoperation of any N relay to the left since the path to the negativeterminal of source 44 is thereby incomplete. The operation of anynoninterference N relay therefore enables a particular line circuit togain exclusive control of the signal path to the receiver controlcircuit 48 and thereby to the apparatuses controlled by circuit 48.

The operation of relay N1 in response to the transfer of contact ST1-1causes contacts N1-1 and N1-2 to transfer from conductors 36, toconductors 39, 40, thereby establishing connections from the A and Bloops to the voltage source 45, via limiter circuit RCL, whichconnections are complete except for a contact TX-l that is still open.Source 45 supplies transmitting current to one of the pairs of linecircuits 1 and 2 after the starting current has terminated. It will beobserved that on the closing of contact 'TX-1 the negative side ofsource 45 is to be coupled to the A loop through make contact N1-1, andthe positive side of source 45 is to be coupled to the B loop throughcontact N1-2. Therefore, when contact TX1 is ultimately closed, thepolarity of the transmitting current through line circuit 1 is oppositeto that of the starting current.

It is evident that operation of a transmitter in line circuit 2 wouldcorrespondingly result in the energizing of starting relay ST2 incircuit 37-2 to reverse the line current polarity in line circuit 2 viacontacts N2-1, N2-2 and conductors 39 and 40, and to operate thenoninterference relay N2 in circuit 110.

The opening of contact Nl-S in circuit interrupts the 48 volt supply totiming relay circuit TRC, and thereby activates this circuit. Theopening of contact N1-5 causes the main timing relay TT in circuit TRCto be operated, but if no signal pulse's are received within nineseconds, relay TT will automatically release again. Concurrently, theoperation of a timing unit in circuit TRC is initiated to energizetiming relay TX, after a delay of about one second to allow sufficienttime for any transmitter that has received current for a long enoughtime to charge its capacitor CD-l to complete the operation of the camcontrolled contacts, K1-1, K1-2, K1-3. The energizing of relay TX andthe consequent closure of contact TX-l between conductor 39 and thenegative side of limiter RCL, as shown in FIG. 2, permits transmittingcurrent of polarity which is the reverse of the starting current to besupplied to transmitter nearest on the line to the current supplied fromthe control center 100. The A loop is now negative and a second ortransmitting charging current path may be traced from contact N1-1through rectifier REC-6, the coding mechanism 27, and operated contactK1-3 to the capacitor CD-l, and from capacitor CD-l to the operatedfront contacts of Kl-l to the positive B loop. The normally open contactK1-3 has been provided to prevent excessive current drain throughpossible ground leakage from the terminals of other transmitters on theline when the supply polarity is reversed. Any leakage to ground in theactuating devices will appear as a partial ground point at the armature41, and, unless the reverse current path through the transmitters iskept open, the cumulative effect thereof could interfere with properoperation of a transmitter. Leakage or a ground at a particulartransmitter when operating (K1-3 closed) can be readily tolerated, sincesource 45 is not connected to ground, not even through a grounddetector.

Current also flows through the series combination of resistors RX-S,RX-6 and reed relay R and, as before, when the voltage on capacitor CD-1reaches the predetermined level, the relay R operates and the motor Mstarts to transmit lsignals in the second stage or transmitting intervalof its two-stage operation. A Zener diode ZE-1 is connected across themotor M as a means of further limiting the current supplied to themotor.

The coding mechanism driven by motor M causes a signal to be generated,for example, by the opening and closing of a circuit as indicated by thecontacts 27-1 and 27-2, and during breaks in the circuit the powersupply to the motor M is maintained by the capacitor CD-1 aided by powerdrawn from the line via resistor RX-8 (shunting the coding contacts)which provides sufficient energy to maintain the governor controlledmotor at constant speed.

The receiver control circuit 48 operates the repeater relay P inaccordance with the code pulses generated by the coding mechanism 27. Inaddition, circuit 48 also functions as a pulse clipper to produce pulsesof uniform amplitude and is furthermore the means of supportingextraneous induced voltages on the line of short duration whichotherwise might result in false operation.

Contacts (not shown) of repeater relay P control the break timing relayIBT and the make timing relay MT in the pulse timer circuit 51 which isalso powered from the source 44. The release of relay BT is delayedapproximately 130 milliseconds to enable the BT relay to remainenergized during the spaces in the code signal generated by codingmechanism 27, and to release only for spaces having a duration greaterthan a predetermined maximum length. The make timing relay MT issimilarly retarded so as not to release during the transmission ofsignal pulses but to release in approximately 190 milliseconds duringthe long pulse at the end of a signal round.

The repeater relay P acting in conjunction with the break and maketiming relays BT and MT controls the advance of a stepper switch in theprinter control 52 which in conjunction with decoding relays and amagnetic counter sets up the particular signal to be printed, togetherwith the hour, date and year record, by the printer 22. In the case ofalarm signals, the tapper bell 24 provides an audible warning to theoperator that an alarm signal is being received. An appropriate pilotlamp on the lamp panel 23 is also illuminated simultaneously. Provisionis also made, but not shown on the drawing, for a special supervisorypilot lamp to be illuminated by the receipt of an alarm signal. Toextinguish this lamp, the operator must throw a Special Attention switchwhich both extinguishes the lamp and causes an acknowledgement signal tobe printed on the paper tape thereby indicating to the supervisor thatthe alarm signal had been properly received and promptly handled.

In the case of signals from combination lire alarmnightwatchtransmitters as well as restoration (to normal condition afteractuation) signals from alarm transmitters, a second cam on motor Moperates the cam operated contact K2-2 to prevent the sounding of thetapper bell 24. The contact K22 is opened by the second cam with theresult that a long break pulse is transmitted causing relay BT in pulsetimer circuit 51 to release and, in so doing, operate a relay (notshown) which silences the bell.

Contact K2-1 is also transferred by the second cam on motor M after thetransmitter starts running on reverse polarity, so that when thearmature 41 of the actuating device is restored to the normal position,the transmitter will be actuated through the alternate path provided byarmature 41 and contact K2-1 to transmit the usual single roundrestoration signal. At the completion of the single round restorationsignal, the contacts K2-1 and K2-2 are again in their normal position.On the completion of all signals, whether of alarm or supervisorynature,-the back contact K1-1 is closed momentarily to allow a path tobe completed via point 28 so that capacitor CD-1 can discharge throughresistor RX-29, thereby preventing excessive over-run of the motor M atthe end of the signal transmission which might otherwise occur due tothe higher charge on the capacitor resulting from operation on a lowresistance line.

Fault conditions Line circuit 1, line circuit 2, and the common receivercontrol circuit 48 are each powered from separate, un-

grounded sources. Consequently, a ground fault on the line circuits oreven single faults existing simultaneously on more than one line circuitwill not afect the operation of the system. However, multiple faults ona single circuit could seriously affect operation since one or moretransmitters could thereby vbe effectively shorted out of the system.For this reason, each line circuit is provided with4 ground detectorapparatus which will produce audible and visible signals should a groundappear on any line circuit.

Referring to line circuit 1 in FIG. 3A, the two windings G1-1,and G1-2of the ground detector relay G1 are connected across the line terminals32-1, 35-1 with the center point. grounded at 38-1. Each of the windingsG1-1 and G1-21is of high resistance and the windings are connected inseries opposition so that the normal magnetic ux produced in eachwinding balances that in the other and the relay remains normallyreleased. A ground or heavy leakage on the line will cause onewinding'to draw more current than the other, relay G1 will becomeenergized and, through contacts not shown, will illuminate pilot lampPL1 and sound the common buzzer BZ which are connected to the source 44.Similarly, ground or heavy leakage on line circuit 2 will operatethrough the windingsy G2-1 and G22 of ground detector relay G2 toilluminate pilot lamp PLS and sound the common buzzerBZ in a similarmanner.

An open circuit condition occurring on either line circuit willde-energize the associated line supervisory relay S1 or S2 and, throughcontacts not shown, will illuminate either pilot lamp PLI or PLS andsound the common buzzer BZ as in the case of a grounded line. Also, asis usual practice in electrical protection systems, other relays (notshown) are operated to supply potential to 'both ends of the line sothat signals may be received until the break is repaired and the linerestored to the normal operating condition.

A short circuit fault occurring between the A loop and the B loop causesthe afected circuit to switch to the running condition (as if contactsK1-1 were closed) and the associated noninterference relay N willoperate. However, since no code pulses are received with a short circuitfault, the line is automatically switched back to the stand-by conditionafter a short interval of time by the main timing relay 'IT. As long asthe short circuit fault persists, the associated relay N will operateand release and this switching action is repeated and results in theflashing of pilot lamp PL2 for the line circuit 1 or pilot lamp PL4 forline circuit 2. Since this type of fault renders the particular linecircuit inoperative, the line circuit must be removed from the systemuntil the fault is corrected.

Receiver line current limiter (RCL) Referring next to FIG. 2, thisdrawing illustrates in detail the limiter circuit RCL shown in blockform in FIG. 3A. This unit serves both to limit the transmitting currentto a predetermined maximum level, for example, 27 milliamperes, and tolimit the line voltage to a selected level, say 45 volts, in order tominimize the undesirable effects of multiple line leakages to groundwhen the line is switched to the receiver.

A voltage divider consisting of resistors R2-1, RZ-Z and diodes D21,D2-2 provides a selected constant voltage, say 1.4 volts, across thediodes. The transmitting current flows through adjustable resistor R2-3to the emitter of transistor T2-1 and thence to contact N1-2 via point21.

When this transmitting current approaches the predetermined maximumlevel, say the 27 milliamperes previously mentioned, the voltage dropacross resistor R2-3 tends to drive the emitter of transistor T2-1 asnegative as it'S base, at which point transistor T2-1 starts to cut offand consequently increases its Icollector to emitter voltage t0 maintainthe current flow at the predetermined maximum level, say 27milliamperes.

The voltage on the associated line circuit is limited to a selectedlevel, for example, the 45 volts specified above, by transistor 'f2-2.The base of transistor T22 is maintained at -45 volts with respect tothe positive side of the source 45, and the emitter has to be madeslightly less negative than the base or else the transistor starts tocut oit, transistor T2-2 thus limiting the voltage on the line circuitto 45 volts. The emitter terminal 23 of transistor T2-2 is connected tothe armature of contact TX-1, while the collecter terminal Z2 oftransistor T2-2 is connected to receiver control circuit 48, as shown inFIG. 3A.

Anti-jamming circuit If a transmitter is jammed in the sending positionbecause of either an electrical or mechanical fault, it could, unlessprovided for, tie up the line. Since no pulses are being received, thisresults in the release of relay 'IT after the nine second delay, so thatthe line circuit switches back to the stand-by or idle condition nineseconds after the transmitter becomes stalled. However, a secondtransmitter Vwaiting to transmit on the same line circuit can get itscapacitor CD-l charged, since the short produced by the resistor RX-30in the stalled transmitter will allow sufficient current to flow tocharge the capacitor CD-l in the second transmitter. For a specificexample, it will be assumed for descriptive purposes that the stalledtransmitter is transmitter 2-1 in FIG. 3A, and that the second actuatedtransmitter waiting to transmit on line circuit 1 is 3-1, so that thesurge of current through resistor RX-30 in transmitter 3-1 actuates thestarting relay delay circuit 37-1 again. Circuit 37-1 is delayed fourseconds, allowing sucient time for the capacitor CD-1 of transmitter 3-1to become charged, and therefore transmitter 3-1 will start. But nosignal will be received from the second transmitter 3-1 after the linehas been switched to the receiver control circuit 48 with reversed linepolarity because of the presence of the stalled transmitter 2-1 on theline with its open K1-2 contact. Referring now to FIG. 5, the operationby transmitter 3-1 of relay TX in circuit TRC has opened contact TX-Z,and after nine seconds, because of the absence of a signal fromtransmitter 3-1, relay TI de-energizes. The opening of contact rFTF-3 onthe release of TI causes normally operated relay X to release. Therelease of relay X opens contact X-Z, thereby breaking the holdingcircuit for relay M1 through contact N1-6, diode D5-20, and contactM1-1. Referring back to FIG. 3A, the release of relay M1 transferscontact M1-3 to its back contact, thereby to transfer the return side ofthe A loop to the armature of contact N1-3, and this together with thetransfer of contact X-3, causes line power to be applied to the returnside of the A loop through the front contact of N1-3 and back contactM1-3. The release of relay M1 also closes backcontact M1-4, thereby toconnect both sides of the B loop to the terminal 21 of limiter circuitRCL.

The switching of power to the return side of the A loop, which is alsoknown as switching to the so-called McCulloh condition, in effectreverses the direction of the transmitting current through line circuit1 to reverse the usual order in which the transmitters in line circuit 1are given priority in transmitting. Thus by reversing the order oftransmission, transmitter 3-1 is placed ahead of instead of behindtransmitter 2-1 so that transmitter 3-1 transmits its signal beforetransmitter 2-1 is returned to the line. It is to be understood that ifthere were other actuated transmitters 4-1, 5-1, n-l, in addition toactuated transmitter 3-1 and stalled transmitter 2-1 on line circuit,then the reversal of transmitting current would result in the operationof the highest numbered transmitter rst, say transmitter n-l, followedin the reverse of the usual order by transmitter (n-1)-1 and Successivelower-numbered transmitters. Pushbutton PB is provided to restore relayM1 and other M relays for other line circuits to the normal energizedcondition. Relay X is restored to its energized condition when thecircuit is switched back to the standby condition by means of arestoring circuit 50 of suitable construction.

It will be obvious to those skilled in the art that NPN transistors canbe employed as Well as PNP transistors, with appropriate changes inpolarity.

What is claimed is:

1. An electrical protection system which comprises a plurality of codesignal transmitters placed at selected points in a location to beprotected, said transmitters being arranged in groups in which eachgroup includes at least one transmitter, each of said transmittersgenerating a characteristic code signal upon actuation in response tothe occurrence of a selected condition,

means for receiving said code signal generated by each of saidtransmitters,

a plurality of conducting pat-hs, each of said paths being associatedwith a corresponding one of said groups of code signal transmitters, andeach of said paths being provided with a rst loop having an input sideand a return side,

and

a second loop having an input side and a return side,

means for connecting the transmitters in each of said groups oftransmitters to the associated one of said conducting paths in apredetermined order, including trst switching means for successivelyconnecting each transmitter in each of said groups between said rst andsecond loops of the corresponding conducting path, so that eachtransmitter receives transmitting current in said predetermined order onits associated conducting path, and a central station including aplurality of rst potential sources in one-toone correspondence with saidplurality of conducting paths for supplying starting current to thecorresponding conducting paths having one or more actuated transmitters,a second potential source, having rst and second terminals, forsupplying said transmitting current to a conducting path having anactuated transmitter, v means for limiting the current and voltageapplied to each of said corresponding plurality of conducting paths fromsaid second potential source and second switching means for successivelytransferring each of said conducting paths having at least one actuatedtransmitter from its corresponding iirst potential source to saidassociated second potential source to receive said transmitting currentinstead of said starting current, the order in which said conductingpaths are successively transferred depending upon which conducting pathis the first to have an actuated transmitter so that interference isprevented between actuated transmitters associated with differentconducting paths, said second switching means including means forconnecting the rst terminal of said second potential source to the inputside of said rst loop and the second terminal of said second potentialsource to the return side of said second loop so that said transmittingcurrent is supplied to each conducting path in a predetermined directionto reach the transmitters on each conducting path successively accordingto said predetermined order.

2. In `combination with the apparatus defined in claim 1, apparatus forreversing the direction of the transmitting current through any of saidconducting paths in which at 13 least two transmitters have beenactuated but one transmitter has stalled -to prevent any othertransmitter from receiving transmitting current, which comprises thirdand fourth swtiching means associated with each conducting path,

said third switching means being provided with a first contact means forchanging the connection of said first terminal of said second potentialsource from the input side to the return side of the first loop of saidconducting path having a stalled transmitter, and

said fourth switching means being provided with a first contact meansfor changing the connection of said return side of said iirst loop fromsaid input side of said second loop to said first terminal of saidsecond source of potential, and a second contact means for connectingthe input side of the second loop to the return side of said secondloop.

3. Apparatus as defined in claim 1, in which said means for limiting thecurrent and voltage applied to each of said corresponding plurality ofconducting paths comprises a first transistor provided with base,collector, and

emitter terminals, said collector terminal being connected to saidconducting path,

a second transistor provided with base, collector, and

emitter terminals, said emitter terminal being connected to saidconducting path, and said collector ter-minal being connected to saidreceiving means,

a voltage divider connected between said positive and negative terminalsof said source of potential,

means for connecting the base terminals of said iirst transistor andsaid second transistor to said voltage divider to -maintain the baseterminal of said first transistor at a first preset voltage and the baseterminal of said second transistor at a second preset Voltage,

anadjustable resistor for connecting said positive terminal of saidsource of potential to said emitter terminal of said first transistor sothat as said current applied to a conducting path having an actuatedtransmitter approaches a predetermined maximum level, the voltage acrosssaid adjustable resistor causes said emitter terminal of said firsttransistor to tend to become `as negative as its base terminal, therebyto cause said first transistor to start to cut ofi and to increase thevoltage between said collector and emitter terminals to maintain saidcurrent at said predetermined maximum level, and

means for connecting said emitter terminal of said second transistor tosaid voltage divider to maintain said emitter terminal slightly lessnegative than said base terminal of said second transistor so that saidsecond transistor starts to cut ofi in response to an increase involtage applied to said conducting path having an actuated transmitter.

4. Apparatus as defined in claim 3 wherein said voltage dividercomprises a first diode provided with first and second terminals,

a second diode provided `with iirst and second terminals,

a rst resistor provided with iirst and second terminals,

a second resistor provided with first and second terminals,

means for connecting said first terminal of said first diode to saidpositive terminal of said source of potential,

means for connecting said second terminal of said first diode to saidlirst terminal of said second diode,

means for connecting said second lterminal of said first resistor tosaid first terminal of said second resistor,

means for connecting said second terminal of said second resistor tosaid negative terminal of said source of potential,

means for connecting together said second terminal of said second diode,said first terminal of said first resistor, and said base terminal ofsaid first transistor, and

means for connecting together said second terminal of said firstresistor, said first terminal of said'second resistor and said baseterminal of said second transistor, and

wherein said means for connecting said emitter terminal of said secondtransistor to said Voltage divider comprises means for connecting thesecond terminal of said second resistor to said emitter terminal of saidsecond transistor.

References Cited UNITED STATES PATENTS 2,109,273 2/ 1938 Meuhter 340-2952,390,222 12/ 1945 Meuhter 340-287 2,832,900 4/1958 Ford 317--33 X3,154,775 10/ 1964 Ghersi 340-292 M. R. SLOBASKY, Assistant ExaminerU.S. C1. X.R. 340-292, 295

V Po-1o5o (fi/69) Patent No 3 1500 Q 377 UNITED STATES PATENT OFFICEInventor(s) Manfred w.

Datemsmhildii' Muehter It is certified that error appears in theabove-identified patent and that said Letters Patent. are herebycorrected as shown below:

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Atwstng Officer "Alarms" should read Alarm-- crosses" should read-passesafter "fault" insert between the control center and thetransmitter thus-- curent should read current-- after "36," insert 36'"supporting" should read suppressing-- SIGNED AND SEALED WILLIAMEISGHUYIME, JR. C'omissionor of Patents

